PRIOR ART
Noble gas leak detectors for detecting infinitesimally small leaks by means of inert noble tracer gases such as helium, argon, neon and the like, preferably helium, are known. One such detector is shown in U.S. Pat. Nos. 3,070,992 and 3,227,872. The leak detector disclosed in those patents has a mechanical pump and a diffusion pump to evacuate the system, a pressure gauge tube, a mass spectrometer to detect gaseous material and a getter pump to remove active gases during the leak checking process.
The leak detector shown in those patents was actually marketed by Vacuum Instrument Corporation ("VIC") of Long Island. The leak detector of those patents uses a titanium sublimation getter pump to remove the active gases and to hopefully leave the noble gases for leak detection. In using the VIC getter pumps helium may be entrapped under the titanium that is evaporated off of a filament, which allows helium later to slowly evolve. That slow evolution of helium causes undesirable helium background. The leak detector of those patents also uses a discharge gauge to measure the pressure in the system. Helium can either diffuse through the glass envelope of the gauge tube or desorb from its inner surfaces or perhaps both. That helium desorption will also cause unwanted helium background. Elastomeric O-rings were also used in connection means in the leak detector of those patents. The O-rings allowed helium to penetrate through the system which also causes high helium background. The leak detector as marketed in accordance with the foregoing patents was to have achieved a leak detection rate of 1.times.10.sup.-14 atm cc/sec of helium. But because of the high helium background in the system, it could only repeatedly detect leaks larger than 10.sup.-12 atm cc/sec.